Effect of embedding depth on decomposition course of crop residues in rice-wheat system

Wheat and rice straw were enclosed in nylon nets and returned to rice and wheat field,respectively,to study the effect of embedding depth(0,7,14 cm) on decomposition course and C/N ratio of crop residues in wheat-rice rotation system.The results showed that rice straw embeded into soil layer of wheat field decomposed faster than surface mulching,and rice straw had the highest decomposition rate at embedding depth of 14 cm.Wheat straw embedded in rice field decomposed faster than rice straw in wheat field,due to the existence of water layer,higher moisture and temperature in rice field,but mulched wheat straw decomposed slower than that of being embedded.After decomposition for one crop season,the residual rates for mulched and embedded rice straw were 60% and 40%,respectively,while the residual rates for mulched and embedded wheat straw were 25% and 20%,respectively.During the course of decomposition,C/N ratio decreased due to the loss of total C.The C/N ratio of rice straw in surface layer of wheat field remained high,while that of wheat straw was the lowest in surface layer and was the highest in mid-layer of rice field.The C/N ratio of rice and wheat straw after one crop season was about 30 and 15,respectively,higher than that of humus,indicating that the humification process was not accomplished.